1. Field of the Invention
The present invention relates to a continuous process for separating organic compounds contained in an extract based on polarity. More particularly, the present invention relates to a commercial process whereby a target compound of interest may be purified by removing undesirable compounds that are more polar or less polar than the target compound.
2. Description of the State of Art
The word "Gin-seng" or "jen-shen" translates from Chinese to "essence of the earth in the form of a man" due to the root's resemblance to the human body. Its widespread use is based upon traditional medicine's belief that ginseng has a unique ability to promote a balance of body and spirit. While the genus Panax contains six species native to Asia and two native to North America, almost all of the commercially available Panax ginseng root is cultivated in the northeastern district and other regions of China and Korea.
Only the roots of Panax ginseng are used medicinally. The main root is a fleshy tap root, branched into smaller rootlets. At the age of 4 to 6 years, when most of the cultivated plants are harvested, their roots usually are about 2 to 3 centimeters in diameter and about 10 to 20 centimeters in length.
Research has identified several classes of compounds in Panax ginseng that are believed to act on the body in a number of beneficial ways. The ginsenosides, a family of saponins, are believed to be the most important. The ginsenosides are made up of two groups, Rg and Rb, each containing several related compounds. Studies have indicated that most of the physiologic effects of ginseng can be related to the ginsenosides.
The Rg group consists of derivatives of protopanaxatriol and includes Rg.sub.1, Re, Rf, Rg.sub.2, and several other related compounds. This group is believed to possess the stimulatory effect on the central nervous system.
______________________________________ Rg Group ##STR1## Ginsenoside R.sub.1 R.sub.2 ______________________________________ Rg.sub.1 D-Glucose D-Glucose Re L-Rhamnose-(.alpha.-1-2)-D-Glucose D-Glucose Rf D-Glucose-(.beta.-1-2)-D-Glucose H Rg.sub.2 L-Rhamnose-(.alpha.-1-2)-D-Glucose H ______________________________________
The Rb group consists of derivatives of protopanaxadiol and includes Rb.sub.1, Rb.sub.2, Rc, Rd, and several other related compounds. This group is believed to possess the depressant effect on the central nervous system.
__________________________________________________________________________ Rb Group ##STR2## Ginsenoside R.sub.1 R.sub.2 __________________________________________________________________________ Rb.sub.1 D-Glucose-(.beta.-1-2)-D-Glucose D-Glucose-(.beta.-1-6)-D-Glucose Rb.sub.2 D-Glucose-(.beta.-1-2)-D-Glucose L-arabinopyranoside-(.alpha.-1-6)-D-Glucose Rc D-Glucose-(.beta.-1-2)-D-Glucose L-arabinofuranoside-(.alpha.-1-6)-D-Glucose Rd D-Glucose-(.beta.-1-2)-D-Glucose D-Glucose __________________________________________________________________________
One of the best studied and documented activities of ginseng is its ability to act as a stimulant and anti-fatigue agent. Further studies have also indicated that Panax ginseng could increase locomotion activity and modify feline EEG recording. Panax ginseng's adaptogenic effects are believed to be due to the action of ginsenosides on the adrenal cortex and on the brain. In 1985, Saito found, from studies with mice and organ cultures, that ginsenoside Rb.sub.1 plays an important role in the catecholamine synthesis of catecholaminergic neurons of the brain, in the ganglion and in the chromaffin cells of the adrenal cortex, as well as in the formation of nerve fibers and in the function of the sympathetic nerve endings. The foundation of these various nerve fibers are important in maintaining glucocorticoid secretion, which regulates the bodies ability to deal with stress. Rg.sub.1, on the other hand, is believed to play an important role in the memory and in sexual behavior. Also, a significant release of adrenocorticotropic hormone (CTH) by rat pituitary cell cultures was observed after doses of Rg.sub.1 by Odani et al. in 1987. Tsang et al. were able to show that a total ginsenoside extract can influence brain functions and behavior patterns.
Panax ginseng may also have the ability to enhance the body's natural immune system by increasing the rate of phagocytosis. Several types of white blood cells are generically known as "phagocytes." Phagocytes attack, engulf and release powerful enzymes that destroy invaders in the blood stream, including microorganisms and pathogens through a process referred to as phagocytosis.
Panax ginseng plants are treated during their growing season with numerous herbicides and fungicides which ultimately always lead, regardless of their form, to residues in the ginseng product, even though sometimes in minute amounts. These residues are understandably undesireable in every case, as is underlined by the intensive public debate surrounding their use. Raw materials used in the production of medicinal products are especially subject to critical evaluation since medicinal products have proven, on account of the demand for purity, to be a very sensitive consumed substance. Consequently, it would be considered advantageous, if it were possible, to produce medicinal products extracted from natural products, having a very low residue content.
Quintozene is a technical-grade preparation of the chlorinated benzene derivative pentachloronitrobenzene (PCNB). PCNB is used as a herbicide and fungicide for seed and soil treatment, and as a slime inhibitor in industrial waters. PCNB has been found in drinking water, well water, crop land and nursery soils, spinach leaves, cheese, fruits, ground grains, leaf and stem vegetables, nuts, oil seed by-products and more recently in ginseng products. The most probable route of human exposure to PCNB is through the ingestion of contaminated food.
Technical-grade PCNB contains impurities. The specific impurities and their amounts depend on the manufacturer and the manufacturing procedure. The relevant impurities are pentachloroaniline (PCA), pentachlorothioanisole (PCTA), and hexachlorobenzene (HCB), because they have also been recently detected as contaminants of ginseng and because they are metabolites/contaminants of PCNB.
Toxicity of PCNB is observed in animals and humans only at doses in the multiple mg/kg body weight range. The acute lethal dose for humans is estimated to be 500 mg/kg or greater. There is no information available on the long-term health effects of quintozene in humans, but the lowest chronic daily dose found to elicit liver changes of dogs is 4.5 mg/kg/day.
The EPA-established Reference Dose (RfD) for quintozene is 0.003 mg/kg/day. EPA estimates that consumption of this dose or less over a lifetime would not likely result in the occurrence of chronic, noncancer effects. This RfD is based on liver toxicity in dogs, including increased liver weight and effects on liver enzymes. EPA has medium confidence in the RfD because the principal study on which the RfD is based appears to be of fair quality, and because of the lack of a complete database on chronic toxicity. The EPA allowable daily intake (ADI) is 0.007 mg/kg/day, and the allowable daily intake from the UN CODEX Alimentarius is 0.01 mg/kg/day. The health risk posed by any chemical, even a carcinogenic compound, depends on the dose at the target site of action as well as its potency in producing an adverse health effect.
PCNB has been observed to bioaccumulate in tissues only at trace or very low concentrations. Two of its metabolites, PCA and PCTA, likewise do not significantly bioaccumulate in tissues. HCB, on the other hand, has significant bioaccumulation. Early toxicity studies of quintozene (PCNB) attributed toxicity to PCNB; however toxicity was most probably due to the contaminant HCB. It is unclear at this time if HCB contributed to tumor production in PCNB carcinogenicity studies. The reported teratogenic activities of PCNB in mice and rats were also most probably due to contamination with HCB because purified PCNB and PCA were not teratogenic.
A variety of different methods for isolating and purifying nonpolar compounds from natural substances including ginsenosides with the simultaneous separation of undesireable contaminants such as pesticide residues have been published. For example, Forster, et al. in their U.S. Pat. Nos. 4,842,878 and 4,946,695 describe the production of hop extracts with a low content of pesticides from hops which are laden with pesticides. In their process, in a first step, the pesticides and the component materials of the hops are extracted with compressed gases and, in a subsequent step, there is carried out a separation of extract and pesticides with the aid of a solid adsorption agent. However, the supercritical carbon dioxide which is utilized is not an efficient solvent for the ginsenosides. A further disadvantage is the insufficient selectivity of the adsorption agent since, besides the pesticides, desired hop component materials are also adsorbed and thus the yields are reduced.
Furthermore, it is known to remove pesticides from senna leaves with dry, supercritical carbon dioxide in which case the content of chlorinated pesticides is reduced by up to 98% without the polar active materials, the sennosides, being co-extracted. However, the application of the process which is successful in the case of senna leaves to ginseng roots has proved to be impossible. The ginsenosides, regarded as being the active materials, are admittedly not extracted with supercritical carbon dioxide but the chlorinated pesticides are also not removed in a satisfactory manner. Thus, for example, quintozene, which is regarded as being the main contaminant of ginseng roots and thus a leading substance for undesired, lipophilic, chlorinated pesticides, is only reduced to about 30% so that the extracted ginseng roots do not even approach the region of commercial usefulness when the pesticide content exceeds the permitted values.
Sch.upsilon.tz, et al., in their U.S. Pat. No. 5,093,123, describe a method of extracting pesticides from ginseng roots using carbon dioxide. However, for this method to function, the moisture content of the roots requires adjustment followed by extracting the moistened root with carbon dioxide at a pressure of more than 100 bar.
The above U.S. Patents, issued to Forster et al. and Sch.upsilon.tz et al., are just a couple of examples of the processes that currently exist in the literature, whereby ginsenosides are extracted, isolated and purified from various plant materials. However, each process disclosed involves multiple steps, which require fairly extreme conditions to function and various solvents. Consequently, the disclosed laboratory scale processes are not easily scaled up to an efficient commercial process where disposal considerations of various solvents play an important role in the overall feasibility of the process. A further disadvantage of the processes as disclosed in the literature is the requirement of using super critical CO.sub.2 in combination with high pressures.
There is still a need, therefore, for a process and procedure for removing undesireable residues that may be toxic from natural substances that are produced for consumption.